Apparatus for evaporation by levitation in an ultravacuum

ABSTRACT

An apparatus for deposition of thin coatings on substitutes by evaporation of solid material in an ultravacuum. The apparatus has an inductor to effect levitation and heating of the material to be evaporated and a transfer device to bring a succession of such pieces into position. The transfer device is operable from the outside of the device by use of two bars which pass through seals in the wall of the device.

United States Patent Inventors Jean Van Audenhove M01; Jean Joyeux; Maurits Parengh, Geel, Belgium Appl. No. 808,580 Filed Mar. 19, 1969 Patented Apr. 13, 1971 Assignee European Atomic Energy Community (Euratom) Brussels, Belgium Priority Apr. 5, 1968 Belgium 56808 APPARATUS FOR EVAPORATION BY LEVITATION IN AN ULTRA-VACUUM 7 Claims, 2 Drawing Figs.

US. Cl l18/49.5, 118/319, 118/500, 118/620, 219/75 Int. Cl C23c 13/12 Field of Search 118/49.1,

[56] References Cited UNTTED STATES PATENTS 2,584,660 2/1952 Bancroft 1 17/932 2,686,864 8/1954 Wroughton et al. 219/75 3,173,283 3/1965 Vogtmann 219/7.5X 3,290,567 12/1966 Gowen 117/93.4 3,476,170 11/1969 Christian et a] 2l9/7.5X FOREIGN PATENTS 1,273,518 9/1961 France 1l8/49.1

Primary Examiner-Morris Kaplan Attorney-Stevens, Davis, Miller and Mosher ABSTRACT: An apparatus for deposition of thin coatings on substitutes by evaporation of solid material in an ultravacuum. The apparatus has an inductor to effect levitation and heating of the material to be evaporated and a transfer device to bring a succession of such pieces into position. The transfer device is operable from the outside of the device by use of two bars which pass through seals in the wall of the device.

APPARATUS FOR EVAPORATION BY LEVITATION IN AN ULTRA-VACUUM This invention relates to apparatus whereby thin coatings can be deposited by evaporation by levitation on any substrates in an ultravacuum (e.g. 10 to 10 Torr).

The technique of evaporation by levitation in a vacuum has already been used but for some applications (e.g. the preparation of ultrapure coatings without contamination) ultravacuum evaporation is necessary. This gives rise to technological problems which are more difi'icult to solve. Also it is important to prevent the ultravacuum from being disturbed too frequently since it takes a long time to restore. The apparatus should therefore provide the possibility of enabling a number of consecutive evaporations to be carried out without interrupting the vacuum.

During all the required operations the vacuum chamber must remain absolutely hermetically sealed. The chamber must also be of small dimensions in order to reduce degasification due to desorption and hence the capacity of the pumps and pumping time required. The mechanisms in the vacuum must also be very well designed to prevent any seizing because all the surfaces must be absolutely clean and the use of some alloys or antifriction materials is prohibited. The reason for this is that they contain lubricating metals which have an excessive vapor tension in an ultravacuum and hence evaporate. The use of graphite is also prohibited because of its porosity: it desorbs large quantities of gas.

If the dimensions of the chamber are to be reduced, the mechanisms inside the chamber must be miniaturized. Seals must be very accurate and the mechanisms must be simple.

The apparatus according to the invention comprises an ultravacuum chamber provided with at least one window or hatch, a mask covering said window within the chamber and movable to uncover the window, a substrate support, an inductor for effecting levitation and heating of the material to be evaporated, a transfer device operable to bring a succession of pieces of material to be evaporated to a station beneath the in ductor, the transfer device embodying upwardly removable carriers for the material pieces, means operable from outside the chamber for operation of the transfer device and comprising a first bar passing through the chamber wall with a vacuum seal and arranged for rectilinear lengthwise movements, and raising means operable from outside of the chamber by a second bar or rod passing through the chamber wall with a vacuum seal and arranged for lengthwise movement, said raising means fulfilling simultaneously two functions, one to move the mask to uncover the window and the other to raise a carrier and material piece from the transfer device to position the carrier accurately on the inductor axis and then to locate the material piece within the inductor.

The invention will be more readily understood by reference to the accompanying drawings on which:

FIG. 1 is a general view of a specific example of the apparatus according to the invention, and

FIG. 2 is a section through a vertical plane of a material holder used in the apparatus shown in FIG. 1.

FIG. 1 shows part of the wall 1 of the vacuum chamber, or more precisely, part of the base thereof. The chamber is provided with viewing windows or hatches 2 which need not necessarily be diametrically opposite. A substrate carrier 3 is disposed above an inductor 4 which is intended to ensure levitation and heating of the material pieces which are to be evaporated. A reception crucible 29 and the pieces or charges 5 for evaporation situated in material holders 6 are disposed on a transfer device, which in the case of FIG. 1 is a turret rotated by a rack and pinion system 7-8, the rack being cut in a bar 9 which extends through the chamber wall by means of a metallic bellows seal similar to the types used commercially for ultravacuum valves and not illustrated in FIG. 1. The turret 10 can thus be rotated simply by a rectilinear movement of the bar 9 from outside. The turret is so disposed that each of the holders 6 can be brought beneath the inductor and approximately in line with its axis.

A rod 12 extends through the wall 1 via a seal at 19 (consisting of metal bellows not shown in detail). Like the bar 9, the rod 12 can undergo only rectilinear axial movements which are controlled from outside by the operator. Inside the chamber, the rod 12 has an extension 13 of smaller section so that there is a shoulder 14 at their junction. The rod extension 13 is in turn continued in the form of a hollow cylinder 15 of a nonconductive and nonporous material, e.g. quartz or Pyrex" glass. The rod 12-13-15 is in line with the inductor axis 11 and can perform movements along this axis only.

The rod extension 13 extends through a weight in the form of a cylindrical bush 16 which can slide freely around it. The internal surface of the weight is formed with a helical slot 17 in which engages a pin or lug 18 secured to the rod extension 13. The wall 1 is formed with a recess 20 which acts as a seat for the weight. Rods 21 are secured to the outer surface of the weight and carry masks 22 adapted to cover the windows 2.

FIG. 2 shows more particularly and in greater detail a suitable material-holder 6 for use in the apparatus described with reference to FIG. I. This material-holder is intended for transport of a sample 5. It is in the form of a hollow cylindrical member 6 with a radial flange 23. The material-holder is disposed in a circular hole 24 of a radius between the radius of the flange 23 and the radius of the cylinder 6 so as to allow the material-holder some freedom of movement. Inside the material-holder is a shoulder 25 which serves as an abutment for a plug 26 which has a head and pointed stem somewhat like a drawing pin, is of nonconductive and nonporous material, e.g. quartz, and serves as a carrier or crucible in which the metallic charge 5 for evaporation is disposed. The plug 26 is so dimensioned that it can slide upwardly inside the materialholder. Its point is so dimensioned that it fits in the tube 15 described hereinbefore (FIG. 1). The bottom part 27 of the material-holder 6 is internally frustoconical or flared so that it can be centered about the tube 15 during the ascent of the latter. The portion 28 of the material-holder has an inside diameter such as to allow vertical sliding therein of the tube 15.

The above-described apparatus operates as follows. After chamber 1 has been evacuated to an ultravacuum by means of pumps (not shown), a material-holder 6 carrying in a carrier or plug 6 a piece of material to be evaporated is brought into a substantially centered position about the axis 11 by operation of the control bar 9 from outside. The operator then actuates rod 12 upwards so that the weight 16 is turned by the action of gravity and the nut and screw system fonned by the lug 18 and the slot 17. The masks 22 at the ends of the rods 21 will then free the windows 2. The pitch required for the helical slot 17 depends upon the movement required of the masks. The shoulder 14 engages and lifts the weight 16 after the lug 18 has covered the entire length of the slot less a distance equivalent to the diameter of the said lug. It is preferable for the latter not to leave the slot since otherwise, after leaving the interior of the weight, the latter would be able to turn either by inertia or as a result of vibration through an angle sufficient to make it impossible to return to the bottom position, the top entrance of the slot no longer being situated vertically beneath the lug.

The movement then continues upwardly and the tube 15 is introduced into the material-holder from the bottom.

Since the latter is simply supported on the turret 10 by its flange 23, it can slide laterally in the hole 24 and thus be progressively centered around the tube 15 and hence with respect to the axis 11 during the ascent of the tube.

Centering of the charge or material piece 5 in two stages, namely a coarse centering by means of the bar 9 actuating the turret 10, followed by fine centering by movement of the holder 6 during the ascent of the rod 13, is used in order to avoid the need for a micrometer screw system. A system for such a type requires greater accuracy in the construction of the mechanism and much closer assembly tolerances, with the resultant risk of seizing in systems in an ultravacuum. Also,

since the atmospheric pressure acting on the metallic bellows results in a force (approximately 5 kg.) which tends to push the bar 9 towards the inside of the chamber, the use of a micrometer system would require a system to be used to counteract this force.

After fine centering of the material-holder, the tube 15, which continues its movement, engages the point of the plug or carrier 26 and lifts the plug until it is brought into the center of the induction coil 4. High-frequency current is then fed into the latter and the material is levitated. After the rotation of the masks 22 the operator can monitor by usual observation the centering of the material-holder around the tube and the levitation of the material into the center of the inductor 4.

When this has been done, the operator simply lowers the tube 15 which deposits the plug 26 on the holder and which, at the end of its movement, returns the masks to the position in front of the windows. Evaporation then begins and the windows remain completely free of any vapor deposit (which is deposited on the masks), so that the windows retain their transparency.

While evaporation continues, the crucible 29 intended to receive the metallic charges when evaporation is discontinued is brought beneath the inductor by rotation of the turret. Evaporation is stopped (and the molten drop falls into the crucible) by cutting off the HF current. The above-described cycle can be immediately repeated with a fresh metallic charge without breaking the vacuum.

From the foregoing description it will readily be seen that the apparatus according to the invention is of very simple construction. Only two seals permitting rectilinear movement are required to provide for changes of pieces for evaporation, their positioning in the inductor, and the movements of the window masks.

In the above-described exemplified embodiment, the transfer device is a turret but of course any plate formed with apertures 24 and whose movements can be controlled from outside simply by a translatory movement can be used without departing from the scope of this invention.

We claim:

1. Apparatus for deposition of thin coatings on substrates by evaporation in an ultravacuum of solid materials which apparatus comprises an ultravacuum chamber provided with at least one window or hatch, a mask covering said window within the chamber and movable to uncover the window, a substrate support, an inductor for effecting levitation and heating of the material to be evaporated, a transfer device operable to bring a succession of pieces of material to be evaporated to a station beneath the inductor, the transfer device embodying upwardly removable carriers for the material pieces, means operable from outside the chamber for operation of the transfer device and comprising a first bar passing through the chamber wall with a vacuum seal and arranged for rectilinear lengthwise movements, and raising means operable from outside of the chamber by a second bar or rod passing through the chamber wall with a vacuum seal and arranged for lengthwise movement, said raising means fulfilling simultaneously two functions, one to move the mask to uncover the window and the other to raise a carrier and material piece from the transfer device to position the carrier accurately on the inductor axis and then to locate the material piece within the inductor.

2. Apparatus according to claim 1, characterized in that each material holder consists of a tubular cylindrical member having on the outside a radial flange and on the inside a shoulder in the form of a circular ring adapted to support a carrier or crucible containing the material for evaporation, the bottom end of the cylinder being internally of frustoconical shape.

3. Apparatus according to claim 2, characterized in that the carrier or crucible containing the sample for evaporation is a drawing-pin-shaped plug of quartz of an outside diameter such that it can slide in the top part of the material-holder situated above the shoulder.

4. Apparatus according to claim 2, characterized in that the transfer device is formed with holes whose diameter is between that of the flange and the outside diameter of the tubular cylindrical member.

5. Apparatus according to claim 1 characterized in that the transfer device is a turret, rotation of which is effected by a pinion engaged by a rack to which rectilinear movements are given by said first bar.

6. Apparatus according to claim 3, characterized in that the said raising means consists of an extension of said second bar or rod in the form of a hollow cylindrical tube made of a nonconductive and nonporous material of a thickness and section such that it can be introduced from below into the material holder and engage the plug.

7. Apparatus according to claim 1 characterized in that for moving the mask to uncover the window there is a lug secured to an extension of the second bar or rod which extension is of a smaller section than the rod of which it forms the extension, so that a shoulder is formed at their junction, and there is a cylindrical bush surrounding the said rod extension, freely slidable along said extension rod and formed with a helical slot in its internal surface and engaging the said lug, the external surface bearing at least one rod supporting the said mask. 

1. Apparatus for deposition of thin coatings on substrates by evaporation in an ultravacuum of solid materials which apparatus comprises an ultravacuum chamber provided with at leaSt one window or hatch, a mask covering said window within the chamber and movable to uncover the window, a substrate support, an inductor for effecting levitation and heating of the material to be evaporated, a transfer device operable to bring a succession of pieces of material to be evaporated to a station beneath the inductor, the transfer device embodying upwardly removable carriers for the material pieces, means operable from outside the chamber for operation of the transfer device and comprising a first bar passing through the chamber wall with a vacuum seal and arranged for rectilinear lengthwise movements, and raising means operable from outside of the chamber by a second bar or rod passing through the chamber wall with a vacuum seal and arranged for lengthwise movement, said raising means fulfilling simultaneously two functions, one to move the mask to uncover the window and the other to raise a carrier and material piece from the transfer device to position the carrier accurately on the inductor axis and then to locate the material piece within the inductor.
 2. Apparatus according to claim 1, characterized in that each material holder consists of a tubular cylindrical member having on the outside a radial flange and on the inside a shoulder in the form of a circular ring adapted to support a carrier or crucible containing the material for evaporation, the bottom end of the cylinder being internally of frustoconical shape.
 3. Apparatus according to claim 2, characterized in that the carrier or crucible containing the sample for evaporation is a drawing-pin-shaped plug of quartz of an outside diameter such that it can slide in the top part of the material-holder situated above the shoulder.
 4. Apparatus according to claim 2, characterized in that the transfer device is formed with holes whose diameter is between that of the flange and the outside diameter of the tubular cylindrical member.
 5. Apparatus according to claim 1 characterized in that the transfer device is a turret, rotation of which is effected by a pinion engaged by a rack to which rectilinear movements are given by said first bar.
 6. Apparatus according to claim 3, characterized in that the said raising means consists of an extension of said second bar or rod in the form of a hollow cylindrical tube made of a nonconductive and nonporous material of a thickness and section such that it can be introduced from below into the material holder and engage the plug.
 7. Apparatus according to claim 1 characterized in that for moving the mask to uncover the window there is a lug secured to an extension of the second bar or rod which extension is of a smaller section than the rod of which it forms the extension, so that a shoulder is formed at their junction, and there is a cylindrical bush surrounding the said rod extension, freely slidable along said extension rod and formed with a helical slot in its internal surface and engaging the said lug, the external surface bearing at least one rod supporting the said mask. 